Seroprevalence of COVID-19 antibodies in the cleaning and oncological staff of a municipal clinic

Aim: To prevent shedding of the novel COVID-19 virus in hospitals, strict hygiene measures and surveillance of the staff and patients is mandatory. Studying the available literature, we assumed that monitoring of the cleaning staff may sometimes be a “blind spot” in surveillance. Although the cleaning personnel is not entrusted with the medical and nursing care of patients, the extent of patient contacts in this group may be comparable to medical personnel and even increase in times of a visit ban in many hospitals. The aim of this study was to investigate the prevalence of COVID-19 infections already undergone in this group. Methods: Antibody titers (IgA and IgG) against COVID-19 were measured in the cleaning staff from June 15th to 30th, 2020 in our clinic. Antibodies against COVID-19 were determined using ELISA (EUROIMMUN™, PerkinElmer, Inc. Company). For purposes of comparison, the same procedure was performed in the staff of the oncology ward, who were regarded as an important group due to their high-risk patients. Results: During the study period, 45 members of the cleaning staff and 20 members of the oncology ward were tested. Significantly elevated IgA antibody titers were detected in 1 person in the first group and in 1 person in the second group. Significantly elevated IgG antibody titers were not detected in the first group and in 1 person of the second group. In case of positive or indeterminate testing, swabs for direct virus detection were taken, but were negative in all cases. Conclusion: The prevalence of already undergone infections in both groups is low, as to be expected due to the still low incidence of COVID-19 infections in the German federal state of Thuringia. However, the presence of such antibodies in the cleaning personnel demonstrates the need for equally strict surveillance in this group.


Introduction
The novel infection COVID-19 raises concerns about nosocomial infections and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission from patients to healthcare workers and vice versa, as well as infection of both groups in everyday life. The Thuringia Clinic Saalfeld is a municipal care hospital with presently 618 beds. In an attempt to evaluate the effectiveness of the hygiene measures taken so far in terms of the COVID-19 pandemic, we examined the COVID-19 antibody titers in two groups of clinic employees. The first group examined was the cleaning staff working throughout the house, and the second was the medical and nursing staff of the oncology ward. Given limited financial resources, the reason for this selection was that the epidemiological situation is hardly known in the first group. To our surprise, a Medline search (keywords: COVID-19; cleaning staff/cleaning personnel; hospital hygiene) generated results for professional healthcare workers focusing on outbreak situations (e.g., [1], [2]), but not for hospital cleaning personnel. The decision to investigate the oncological staff resulted from the special risk profile of patients on the oncology ward. The cleaning personnel are not entrusted with the immediate medical and nursing care of the patients, but the extent of patient contacts in this group may be comparable to medical personnel. Furthermore, there is reason to believe that the ban on visits by relatives and acquaintances in many clinics can even lead to an increase in contact between patients and cleaning staff. Obviously, the cleaning personnel in a clinic must also follow the same protective measures as medical personnel when in contact with patients. However, the current trend toward "outsourcing" may result in inadequate communication of information and performance of procedures. Furthermore, these measures may not necessarily be conducted by health professionals or be given to persons who may have limited German-language skills. As for the oncological staff, it is important to consider the well-established risk factors associated with mortality in COVID-19: age [3], hypertension, coronary heart disease, and diabetes [4]. However, this may also include cancer, since the patients are more susceptible to infection due to their immunosuppressive state caused by the malignancy itself and oncological therapies. Given a COVID-19 infection, this may cause a poorer prognosis [5]. However, although some authors demonstrated that patients with cancer might have a higher risk of COVID-19 than cancerfree individuals and that patients with cancer had poorer COVID-19 outcomes, the number of patients investigated was low (n=18) and the authors suggested a nationwide analysis. Preventive strategies in hospitalized cancer patients include the use of disposable personal protective equipment for health workers and patients, social distancing in waiting rooms and wards, prohibiting visitors from accompanying patients, and alerting health workers to minimize the time spent in the hospital rooms [6]. In terms of cancer therapy, is important to consider possibly delaying treatment depending on the tumor biology and staging, converting intravenous treatment to an oral regimen where possible, and adopting less toxic chemotherapy to limit complications requiring re-hospitalization [7], [8]. Recommendations of the European Society for Medical Oncology do of course also include the staff of oncological wards ("Protect yourself to protect your patients") [8]. Despite the restrictions in everyday life, the risk for any member of the hospital staff to become infected in the social or home environment outside the clinic remains unaffected. As for the surveillance of any staff, health diaries with a regular documentation of possible symptoms such as fever or cough are an option. Unfortunately, the insidious onset of the COVID-19 infection (that can manifest without any obvious clinical symptoms, such as fever, in the early phase) and the long incubation period (up to 24 days) limits the effectivity [7]. A regular testing by using oropharyngeal smears using a multiplex realtime PCR with specific gene probes is the "gold standard". Unfortunately, COVID-19 testing may take about a day, is expensive and can be problematic due to limited laboratory capacities. Furthermore the method can have problems in terms of "early" and post negative detection [9]. The value of regular antibody testing is still being discussed [10], and solid data on the extent of active or undergone infections among the staff described are hardly available. Such testing may help in understanding the extent of recently acquired and already overcome infections [11]. Thus, the particular focus of our investigation was to collect data on how many members of the two groups could have already experienced a COVID-19 infection.

Persons and proceedings
After an information session, obtaining informed consent, and with approval by the Ethics Committee of the State Medical Association of Thuringia, we examined the IgA and IgG antibody titers of the housekeeping staff (n=45) and the oncological staff (n=20) (4 doctors, 16 nurses) in our clinic from June 15 th to 30 th , 2020.

Antibodies
An enzyme-linked immunosorbent assay (ELISA) is used for determining antibodies against SARS-CoV-2 (EUROIMMUN™, a PerkinElmer, Inc. company). The assay is CE (Conformité Européenne)-certified and IVD (In Vitro Diagnostic)-approved. The specificity of the test for IgG is given as 98.5% by the distributor and as 92.5% for IgA. Validation in our house was done from known cases of undergone COVID-19 infection. Antibody titers below 0.8 were negative and after discussion with the laboratory doctors, we considered titers of 2 and above to be reliable and significant. Swab SARS-CoV-2 is diagnosed using oropharyngeal smears and a multiplex real-time PCR with three specific gene probes (N, E and RdRp). The abbreviations refer to structural proteins of the coronavirus. These are nucleocapsid protein (N), small envelope protein (E) and RNAdependent RNA polymerase (RdRp). The detection limit is 100 RNA copies/reaction.

Results
The numerical imbalance between the two groups does not allow statistical comparative testing, which is why the data are presented as a table (Table 1). In case of elevated antibodies against COVID-19, an oropharyngeal swab for COVID-19 was performed, which was negative in all cases. Since March 3 rd , 2020, when the first case of SARS-CoV pneumonia was detected in our clinic as well as in the German federal state of Thuringia, only one nurse of the oncological staff reported possible symptoms of COVID-19 infection and was tested positive by PCR (but without transmission to the patients). This is also reflected by significantly elevated IgA and IgG titers. As for the cleaning staff, the person with elevated IgA titers was asymptomatic. It is noteworthy that on the oncology ward, none of the cleaning personnel had significantly elevated antibody titers.

Discussion
According to the website of the Robert Koch Institute, 3,265 cases of COVID-19 infection have been identified in the German federal state of Thuringia [12]. The 7-day incidence is 1 case (accessed July 3 rd ). This means that the incidence of disease is relatively low compared to the total incidence in Germany (195,674 cases as of July 3 rd , 2020). This may be reflected by the rather low frequency of infections already undergone in both groups examined in our clinic. However, our still-limited understanding of the kinetics of rise and fall of antibodies in COVID-19 raises the question of whether antibodies have failed to form in some persons or whether they have already decreased below the detection limit. Examining the timeline of antibody formation and using an ELISA by another distributor, Xiang et al. [11] tested serological IgM and IgG antibodies in 216 serum samples of 85 confirmed COVID-19 pneumonia patients. The IgM and IgG antibodies were detected as positive as early as the 4 th day after onset, and the seropositivity rate of IgM increased gradually. However, IgG increased sharply by the 12 th day after onset. In an attempt to address not only the kinetics of antibody formation in terms of their rise, but also their decline in serum, Sun et al. [13] analyzed longitudinal blood samples from 38 patients (11 intensive [14]. Furthermore, the limits of our current knowledge are illustrated by surprising observations that some people (even hospitalized patients) who present positive results from molecular tests do not have detectable levels of protective IgG antibodies or neutralizing antibodies [14]. Such open questions, concerns and limitations have to be kept in mind when analyzing the data of studies performed to analyze the epidemic situation (focusing on already overcome infections). The current data situation for antibody tests in Germany's general population shows a very inconsistent picture regarding already overcome infections with COVID-19 [15]. For example, the analysis of IgA and IgG levels in the "Heinsberg" study (919 study participants living in 405 households) measured in plasma samples of all study participants by ELISA (EUROIMMUN™) showed 18.5% of the study participants to be IgA positive and 13.6% IgG positive. Contrastingly, in a study in blood donors in Hamburg from April 6 to 10, only one previously unknown SARS-CoV-2 infection was detected serologically (0.3%) in 300 persons; from May 4 to 6, there were two previously unknown cases of SARS-CoV-2 infection in 288 blood donors (0.7%), and from June 2 to 5 with 326 blood donors, again only one previously unknown SARS-CoV-2 infection (0.3%) [16].
In principle, an analysis of COVID-19 antibody titers would be desirable for evaluating the infection status of the entire hospital staff and -combined with molecular testing to detect the most recent infections -obtaining a "complete" epidemiological picture. Our limitation to two groups of people resulted from financial constraints; the selection criteria were justified and described above. Due to the present lack of data, it may also be speculated that the cleaning staff is a blind spot in surveillance. Selecting the oncological staff as the comparison group was based on the particular risk situation of the patients. For similar reasons, areas such as dialysis, neonatal (ICU) stations and transplantation wards would also be of interest.

Conclusion
Our results for the cleaning staff show that antibodies against COVID-19 are detectable, as expected. This emphasizes the need for strict surveillance of this group in hospitals.

Competing interests
The authors declare that they have no competing interests.

Funding
There was no financial support.